Studies on immune regulation made considerable progess. (1)\We defined a common suppressor T-cell pathway in mice and identified three distinct suppressor T cells, Ts1, Ts2 and Ts3, which interact with each other in turn to mediate antigen-specific suppression. (2)\We have shown that the immunosuppressive effects of in vivo ultraviolet radiation are caused by suppressor T cells which develop as a consequence of a transient decrease in the relative number of Ia-bearing antigen-presenting cells. (3)\Considerable advances were made in our understanding of the signals regulating the expression of Ia antigens on antigen-presenting cells. (4)\Progress was made in the isolation and purification of MHC antigens to be inserted into liposomes. Liposomes containing MHC antigens and foreign antigens were then used to stimulate specific immune responses.